Electrolytic conductivity detector system

ABSTRACT

An electrolytic conductivity detector system is disclosed that is particularly useful for gas chromatography. Small gas molecules that will support conductivity are conducted to a gas-liquid contactor where the gas is mixed with a solvent to form a heterogeneous gas-liquid mixture. The gas-liquid mixture is thereafter directed to a gas-liquid separator and a conductivity cell where liquid phase is separated from gas phase and separated liquid phase utilized for conductivity measurement. A unitized gas-liquid separator-conductivity cell may be utilized that includes an inner electrode tube extending upwardly into a larger diameter bore of a metallic outer electrode block, the portion between the block and upper portion of the tube forming a liquid phase reservoir with the liquid phase in the reservoir being utilized for conductivity measurement while between the two electrodes. Three alternate embodiments of a unitized separator-conductivity cell are also disclosed as is a gas-liquid separator and separate conductivity cell. The overall system is small and compact, yet rugged, and is particularly well suited for selective detection of nitrogen, halogen and sulfur containing compounds, although not being limited thereto.

RELATED APPLICATION

This application is a division of my copending U.S. Pat. applicationSer. No. 425,116, filed Dec. 17, 1973, and entitled "ElectrolyticConductivity Detector", which application issued as U.S. Pat. No.3,934,193 on Jan. 9, 1976.

FIELD OF THE INVENTION

This invention relates to an electrolytic conductivity detector systemand more particularly to an electrolytic conductivity detector systemfor gas chromatography.

DESCRIPTION OF THE PRIOR ART

The application of electrolytic conductivity for the determination ofgas chromatographic eluates has been reported by O. Piringer and M.Pascalau in the Journal of Chromatography, Volume 8, page 410, 1962. Inthis reported application, organic compounds were combusted to CO.sub. 2in a furnace containing CuO, the CO₂ dissolved in deionized water in along capillary tube, and the conductivity of the resulting solutionmonitored. The sensitivity of the detector was specified to be betweenthat of thermal conductivity and flame ionization detectors.

A detection system similar to that mentioned immediately hereinabove hasalso been used by D. M. Coulson, as reported in the Journal of GasChromatography, Volume 3, page 134, 1965, for the selective detection ofhalogen, nitrogen, and sulfur containing compounds. The detectordesigned by Coulson, unlike the Piringer and Pascalau detector, wasdesigned to give a low response to carbon containing compounds, and thesensitivity achieved was approximately 1- 5 ng for polyhalogenatedpesticides.

An electrolytic conductivity detector for the determination of chlorine,nitrogen, and sulfur compounds has also been recently described by P.Jones and G. Nickless in the Journal of Chromatography, Volume 73, page19, 1972. The detector described by Jones and Nickless includescomponents similar to that of the detector described by Coulson, bututilizes a commercially available conductivity cell and conductivitymeter that was originally designed for monitoring liquid or ion-exchangechromatography columns to achieve the conductivity measurements. Inaddition, the detector utilized was unlike that of the Coulson detectorin that it employed a specially prepared nickel catalyst for thereduction of chlorine, nitrogen, and sulfur compounds to HCl, NH₃, andH₂ S, respectively, and a dilute HCl solution was used as theconductivity solvent for monitoring Cl and N compounds. Halogenatedcompounds were detected by an increase in conductivity, whereas nitrogencompounds were detected by a decrease in conductivity. A dilute reactiveEtOH--I.sub. 2 --HCl solution was used for the detection of sulfurcontaining compounds (H₂ S+ I₂ → S+ 2HI). Sensitivity to the halogenatedcompounds was found to be approximately ten times that of the Coulsondetector, but sensitivities to nitrogen and sulfur compounds were foundto be similar to that of the Coulson detector.

A conductivity detector based on a modified flame ionization detectorhas also been described in the prior art by J. C. Sternberg and D. T. L.Jones at the Pittsburg Conference of Analytical Chemistry and AppliedSpectroscopy, at Cleveland, Ohio, Mar. 5 through 9, 1970.

Besides the selective determination of compounds containing a specificelement, electrolytic conductivity detectors have also been usedheretofore, at moderate furnace temperatures, for the determination ofcertain compounds containing the same elements. For example, anelectrolytic conductivity detector as designed by Coulson has beenutilized heretofore for the selective determination of chlorinatedhydrocarbon insecticides in the presence of polychlorinated biphenyls,the achieved selectivity being reported as >10⁴, with a furnacetemperature of 710° C. and no reaction gas (See J. W. Dolan, R. C. Halland T. M. Todd, J. Ass. Office, Anal. Chem., Vol. 55, page 537, 1972),and the same type detector has also been utilized with a furnacetemperature of 400°-600° C. for the selective detection ofN-nitrosamines in the presence of other nitrogen compounds (See J. W.Rhoades and D. E. Johnson, J. Chromtogr. Sci., Vol. 8, page 616, 1970).

SUMMARY OF THE INVENTION

This invention provides an electrolytic conductivity detector that issmall and compact yet is rugged and is suitable for gas chromatography.Small molecules that will support conductivity are mixed in a gas-liquidcontactor with a solvent after which liquid phase is separated withconductivity measurement of separated liquid phase then occurring. Aunitized separator-conductivity cell is preferably utilized to provideseparation and conductivity measurement. Enhanced sensitivity andversatility, as well as compactness and simplicity of design andconstruction, are provided.

It is therefore an object of the invention to provide an improvedelectrolytic conductivity detector.

It is another object of this invention to provide an improvedelectrolytic conductivity detector that is small and compact yet isrugged.

It is still another object of this invention to provide an improvedelectrolytic conductivity detector that is suitable for gaschromatography.

It is yet another object of the invention to provide an improvedelectrolytic conductivity detector that has enhanced sensitivity andversatility.

It is still another object of this invention to provide an improvedelectrolytic conductivity detector that has simplicity of design andconstruction.

It is yet another object of this invention to provide an improvedelectrolytic conductivity detector that has an improved electrolyticconductivity detector with an improved gas-liquid separator.

It is still another object of this invention to provide an improvedelectrolytic conductivity detector that has an improved gas-liquidseparator wherein the liquid phase is separated prior to conductivitymeasurement.

It is yet another object of this invention to provide an improvedelectrolytic conductivity detector having a unitized gas-liquidseparator and conductivity cell.

With these and other objects in view, which will become apparent to oneskilled in the art as the description proceeds, this invention residesin the novel construction, combination, and arrangement of partssubstantially as hereinafter described and more particularly defined bythe appended claim, it being understood that such changes in the preciseembodiments of the herein disclosed invention are meant to be includedas come within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate complete embodiments of theinvention according to the best mode so far devised for the practicalapplication of the principles thereof, and in which:

FIG. 1 is a block diagram of the electrolytic conductivity detectorsystem of this invention;

FIG. 2 is an exploded side view of the unitized electrolyticconductivity detector including one embodiment of the unitizedseparator-conductivity cell;

FIG. 3 is a cutaway side view of the preferred embodiment of theunitized separator-conductivity cell of the electrolytic conductivitydetector shown in block form in FIG. 1;

FIG. 4 is a side sectional view of the unitized separator-conductivitycell shown in FIG. 2;

FIG. 5 is a side sectional view of a preferred embodiment of theunitized separator-conductivity cell as shown in FIG. 3;

FIG. 6 is an alternate embodiment illustrating a separate separator anda separate conductivity cell in a side sectional view;

FIG. 7 is a second alternate embodiment of a unitizedseparator-conductivity cell;

FIG. 8 is a third alternate embodiment of a unitizedseparator-conductivity cell;

FIG. 9 is a cutaway perspective view of a reaction furnace that may beutilized with this invention;

FIGS. 10A through C are graphs illustrating detector response tochlorinated hydrocarbon pesticides in the reductive mode;

FIGS. 11A and B are graphs illustrating detection response tochlorinated hydrocarbon pesticides in the oxidative mode;

FIG. 12 is a graph illustrating detector response (peak height) versusgrams of heptachlor;

FIGS. 13A and B are graphs illustrating comparison of microelectrolyticconductivity and flame photometric response to sulfur containingcompounds; and

FIGS. 14A, B, C and D are graphs illustrating detector responseidentifying the preferred embodiment of the separator-conductivity cell.

DESCRIPTION OF THE INVENTION

As shown in the block diagram in FIG. 1, the system for the gaschromatograph electrolytic conductivity detector may include a furnace25 (or other device for the formation of compounds that will supportelectrolytic conductivity), a gas-liquid contactor 26, a unitizedgas-liquid separator-conductivity cell 27, a solvent delivery system 29,and electrical components 30 for measuring conductivity. In this type ofdetection system, a compound is transferred from a supply source, suchas from a gas chromatograph 32, for example, to the furnace where it isdegraded to small inorganic compounds that will support electrolyticconductivity, such as, for example, HCl, SO₃, NH₃, or CO₂. As also shownin FIG. 1, gas from an appropriate reaction gas source 36 may beutilized to carry the compound to furnace 25, and the gas reactionsource is preferably connected to furnace 25 through a conventionalvalve (not shown).

The small gaseous molecules are transported from furnace 25 togas-liquid contactor 26, preferably through glass or Teflon capillarytubing. At gas-liquid contactor 26, the molecules are mixed either withan aqueous or organic solvent. The gas and liquid phases are thenconducted to gas-liquid separator-conductivity cell 27 where the liquidphase is separated from any insoluble gases with the collected liquidphase being then utilized for measurement of the electrolyticconductivity. As will be readily appreciated, the unitizedseparator-conductivity cell functions by having the separator also serveas a concentric electrode conductivity cell. In the unitizedseparator-cell, the heterogenous gas-liquid mixture from the gas-liquidcontactor separates into two smooth flowing homogeneous phases when themixture comes into contact with the inside wall of the detector block ofthe separator-cell. The liquid phase then flows down the wall as asheath with the gas phase as the core. In so doing, the liquid phasepasses between the inside wall of the detector block (outer electrode)and the outside wall of the inner gas exit tube (inner electrode) of theseparator-cell, with the phases then being finally vented through thegas exit tube. Thus, the driving forces that make the separator-cellfunction are the bonding attraction between the liquid phase anddetector surface, the downward forces of the moving liquid phase, andthe positive pressure on the liquid phase in the detector. The principalforce responsible for separation of the gas-liquid mixture is thebonding attraction between the liquid phase and the separator surfaces.By the liquid phase adhering to the separator surfaces, the gases areforced to separate from the liquid phase and formed into a gaseous corethat is vented from the detector. The stated remaining forces that makethe separator-cell function, namely the downward forces of the movingliquid phase and the positive pressure on the liquid phase of thedetector cause the liquid phase to flow between the inner and outerelectrodes. The positive pressure on the liquid phase is due to thecontinuous flow of liquid and gas phases into the detector, while thebonding attraction is the result of the materials used. The bondingattraction of the liquid phase to the separator surfaces is thought tobe the result of known forces such as van der Walls and hydrogenbonding. With metal used for the separator surfaces and with organicsolvents used, van der Walls forces are thought to be more importantwhile hydrogen bonding is thought to play a significant role in the caseof a polar liquid such as water used along with moderately polarseparator surfaces such as glass. Hence materials and geometry areimportant, and metal surfaces seem superior to glass, which, in turn, issuperior to most plastics in achieving separation (glass is superior tometal, however, for separation of gas and water mixtures).

Specificity in electrolytic conductivity detectors can be achieved byreaction gas composition, reaction temperature, use of abstractors, andconductivity solvent. In the oxidative mode, SO₂ -SO.sub. 3, HCl, CO₂,H₂ O, and N₂ are the products produced from compounds containing sulfur,chlorine, or nitrogen. Water and N₂ give little or no response, SO₂ andSO₃ can be removed by a CaO scrubber in the furnace tube, HCl can beremoved by a AgNO₃ scrubber, and the response due to CO₂ can be madenegligible by a very short gas-liquid contact time or the use of anonaqueous solvent. In the reductive mode, H₂ S, HCl, NH₃, and CH.sub. 4are the products obtained from organic compounds containing sulfur,chlorine, or nitrogen. Hydrogen sulfide has too weak of an ionizationconstant to give an appreciable response, HCl can be removed by an acidscrubber such as Sr(OH)₂, and the formation of NH₃ requires a catalyst.Consequently, by the proper choice of conditions high specificity can beachieved for either sulfur, halogen or nitrogen compounds.

As shown in FIG. 1, measurement of conductivity at conductivity cell 27can be made by a conventional conductivity meter 40 and the resultingreadings at the meter can, if desired, be recorded by a recorder 41connected conventionally with meter 40.

Solvent circulating system 29 includes a solvent reservoir 43 whichreceives the solvent passed through the conductivity cell. The liquid ispumped from reservoir 43 by a means of a pump 44, which pump may, forexample, be a Teel No. 1P676 centrifugal pump with the solvent from thereservoir being pumped through a bed of Duolite ARM-381 mixed H/OH ionexchange resin (not shown) to gas-liquid contactor 26. A valve (notshown) can be utilized to regulate flow rate.

An exploded view of a portion of the electrolytic conductivity detectorsystem of this invention is shown in FIG. 2 with one embodiment of theseparator-conductivity cell shown. As shown, gas-liquid contactor 26 ismounted to detector cap 49 with gas-liquid separator-conductivity cell27 being mounted below cap 49. Conductivity cell electrical leads 50 and51 extend upwardly therefrom through detector cap 49 and are connectedwith the conductivity meter 40. A brass solvent splatter shield andinner electrode connector 52 is mounted on inner tube and electrode 53.A stainless steel shield and solvent cup 54 fits over theseparator-conductivity cell 27 and a reservoir cap 55 is positioned atthe bottom of the detector. Cap 55 has a tube 56 extending therefromconnected to inner tube 53 through which solvent is expelled from thedetector. The detector, as shown in FIG. 2, is small and compact andneed have a diameter no greater than about one inch.

FIG. 3 shows a side view of the preferred embodiment of the unitizedelectrolytic conductivity detector system. As shown, the detectorincludes a contractor block 57, preferably of Teflon. Block 57 has abore therein for receiving a solvent delivery tube 58, the boreextending downwardly to the central portion of the block to communicatewith a side bore opening to reaction product delivery tube 60. Thereaction product delivery bore is preferably of the same dimensions asthe solvent delivery bore 58. A solvent-gas delivery passageway 61extends downwardly from the junction of the inlet bores, the deliverypassageway opening into the upper end of the unitizedseparator-conductivity cell 63 (shown in greater detail in FIG. 5).Solvent delivery passageway 61 is preferably of the same dimensions asthe inlet bores. As shown, the unitized separator-conductivity cell 63has an insulating sleeve 64 extending to an inner electrode connectingblock 65 adapted to receive a tube 66 at the lower end through which gasand solvent may be expelled.

The embodiment of the gas-liquid separator-conductivity cell 27 shown inFIG. 2 is shown in greater detail in FIG. 4. As shown therein, outerelectrode and detector block 68 has a bore 69 therein for receiving thegas and liquid mixture from contactor 26. Inner electrode and solventliquid exit tube 53 extends upwardly and partially into the bore 69. Areservoir 70 is formed between the block 68 and the upper portion oftube 53 with solvent being expelled from the reservoir through aperture72 in tube 53 near the bottom of the reservoir to allow solvent removalfrom the separator-conductivity cell 27. Insulating sleeve 74 surroundstube 53 below reservoir 70 and sleeve 74 preferably extends to the upperedge of connector block 52 through which tube 53 extends and iselectrically connected therewith. As can be appreciated from theforegoing, tube 53 (and block 52) and block 68 (inner and outerelectrodes) are thus electrically isolated from one another.

In operation the liquid and gas mixture is received in bore 69 fromcontractor 26. The liquid phase flows downwardly into reservoir 70 wherethe conductivity measurement is obtained by means of the inner and outerelectrodes 53 and 68 (during flow of liquid phase between theelectrodes) connected through leads 50 and 51 to conductivity meter 40.The liquid phase is then expelled from the separator-conductivity cellthrough aperture 72 and tube 53.

The preferred embodiment (63 is identified in FIG. 3) of the unitizedseparator-conductivity cell is shown in detail in FIG. 5. As shown inFIG. 5, the preferred embodiment is like separator-conductivity cell 27except for modified stainless steel connector blocks 76 and 77. Block 77preferably engages the lower end of insulating sleeve 74 at the upperedge and has a cylindrical flange 78 extending outwardly from the loweredge, which flange receives a tube or the like such as shown in FIG. 3.Block 76 has a beveled upper edge so as to be received in the matinglower portion of contactor block 57 as shown in FIG. 3. Operation of thepreferred embodiment is identical to that as described hereinabove withrespect to the embodiment shown in FIGS. 2 and 4.

A still further alternate embodiment for gas-liquid separator andconductivity measurement is shown in FIG. 6 to consist of a separator 80and conductivity cell 81. In gas-liquid separator 80, assembly block 83has an axial bore therethrough, the upper end of which receivessolvent-gas delivery tube 84 and may be, for example, a continuation ofthe solvent-gas delivery tube extending downwardly from gas-liquidcontactor 26. Assembly block 83 may be of stainless steel and the axialbore therein has a larger diameter in the lower portion thereof and hasan upwardly extending gas exit tube 85 received therein. As shown, tube85 extends to a point just below a tapered shoulder 86 forming theenlarged portion of the axial bore in the assembly block. Gas exit tube85 is of smaller diameter than the lower portion of the bore and ispreferably 0.0625 inches outside diameter times 0.030 inches internaldiameter with the spacing between the gas exit tube and the inner wallof the block 83 forming a small reservoir 87 therebetween (the internaldiameter of the bore being preferably 0.0730 inches). A solvent exittube 88, preferably of Teflon having a 0.0625 inch outside diametertimes 0.023 inch internal diameter, is received in a side bore in theassembly block and communicates with the reservoir 87 at or near thebottom thereof. A seal 89, preferably of Teflon, is provided at thebottom of the reservoir extending between the inner wall of the assemblyblock and the outer wall of gas exit tube 85. The gas and liquid phasesenter vertically into the separator 80 through delivery tube 84 and flowdown the outside walls and enter vertically into the small reservoirprovided between the inner wall of the assembly block and the outer wallof gas exit tube 85. The liquid phase collecting in the reservoir isthen withdrawn therefrom through solvent exit tube 88 and conducted toconductivity cell 81.

Conductivity cell 81 is also shown in detail in FIG. 6. As showntherein, a center electrode 91, preferably of 0.0625 inches outsidediameter is received within the axial bore of an outer electrode 92 withcenter electrode 91 being maintained spaced from outer electrode 92 bymeans of Teflon seals 93 at each end of the cell. Near the lower end ofthe cell, a side bore in the outer electrode receives solvent entry tube94, preferably having the same dimensions as solvent exit tube 88 (andconnected thereto) of separator 80 and made also of Teflon. Tube 94supplies liquid phase to passageway 95 in the conductivity cell formedbetween the center and outer electrodes. A second side bore near the topof the conductivity cell receives solvent exit tube 96 for expellingliquid phase from the conductivity cell, the exit tube being preferablyof Teflon and of 0.0625 inch outer diameter times 0.031 inches internaldiameter.

A second alternate embodiment 99 of the unitized separator-conductivitycell is shown in FIG. 7 to include a stainless steel outer electrode anddetector housing 100 with a central bore thereon. A gas-liquid inlet andcenter electrode 101 extends downwardly into the central bore of housing100 and terminates a short distance above a lower Teflon seal 102 at thebottom portion of the bore to form a passageway 103 between the innerand outer electrodes. A gas exit tube 104 extends upwardly within thebore through lower seal 102 and extends partially within centerelectrode 101 so as to form a reservoir 105 therebetween. An upperTeflon seal 106 seals the upper end of the passageway 103 formed betweenthe inner and outer electrodes and a side opening exit tube 108 forsolvent exit opens from the top of passageway 103 below seal 106.

In operation, embodiment 99 receives the liquid and gas mixture throughinlet and center electrode 101. The mixture separates in the tube 101and a liquid phase is received in reservoir 105 and exits therefrom atthe bottom of the reservoir through passageway 109 formed between centerelectrode 101 and lower seal 102. The liquid phase exiting from thereservoir through passageway 109 is introduced into passageway 103 whereit is urged upwardly between the inner and outer electrodes to exit fromsolvent exit tube 108, the conductivity measurement being made of theliquid phase while in passageway 109.

A third embodiment 112 of the unitized separator-conductivity cell isshown in FIG. 8 to include an outer electrode and detector housing 114having a central bore therein, said bore being of reduced diameter atthe top portion 115 to form a gas-liquid inlet. An inner electrode andliquid exit tube 117 extends upwardly into the bore, said innerelectrode 117 being maintained spaced from the outer electrode 114 bymeans of insulating sleeve 118. Inner electrode 117 terminates beforethe reduced diameter portion 115 of the bore and a reservoir 119 isformed between the inner and outer electrodes. A side-opening exit tube120 opens from the bottom of the reservoir to allow liquid phase in saidreservoir to exit from the separator-conductivity cell. Conductivitymeasurement is obtained from liquid phase in the reservoir while betweenthe inner and outer electrodes.

As can be seen from the foregoing, the detector system of this inventionfeatures extremely small size as compared to heretofore known orutilized electrolytic conductivity detectors and may include a smallfurnace on the order of 2" × 2". This is contrasted, for example, to thedetector of Coulson, referenced hereinabove, which utilizes an all glassdetector assembly of about 4" × 26". The detector also includes agas-liquid separator that will function at any angle including beinginverted, has separate 0 to m1 quantities of liquid, and isself-starting and maintaining. The detector system also includes the useof an AC conductivity meter with synchronous detection that preventspeak broadening due to polarization effects and provides a lineardynamic range of at least 10⁵. The detector system also allows the useof nonaqueous conductivity solvent (ETOH) which enables the detector tobe operated in the oxidative mode without solvent venting and provides aselectivity >10⁵. The overall design of the detector system of thisinvention enables the detector assembly to be mounted either at orremoved from the furnace and the small size of the furnace allows it tobe mounted in any location a standard gas chromatograph detector (i.e.flame ionization) can be mounted.

Furnace 25 is shown in detail in FIG. 9 for illustrative purposes. Asshown, furnace 25 includes a furnace housing 125, a quartz reaction tube126, a reaction gas and column eluant gas entrance tee 127, and a teemounting device 128. A reaction tube securing device (not shown) can beutilized. The furnace core includes an alumina tube 129 surrounding thatportion 130 of quartz reaction tube 126 that is within the furnace withthe alumina tube having No. 25 gauge Tophet 30 wire 131 woundthereabout. Insulating filler 132 then surrounds the alumina tube withinthe furnace. The quartz reaction tube 126 is preferably mounted to theinlet tee by Teflon ferrules (not shown) and secured by a stainlesssteel nut 134.

Performance of the detector of this invention as shown in FIG. 8, isillustrated in the various graphs and charts of FIGS. 10 through 13. Thedetector of FIG. 8 was evaluated both in the reductive and oxidativemodes using a Chromatronix conductivity meter. The detector furnace wasoperated at 820° centigrade in the reductive mode and at 840° centigradein the oxidative mode with 1 cc/min of either hydrogen or oxygenreaction gas. Reaction tubes were 6 mm OD× 0.5 mm ID× 150 mm lengthquartz tubes and were used empty with no prior conditioning. Thedetector was mounted on a Tracor MT-220 gas chromatograph and interfacedto the column exit by approximately six inches of 1/16 inch stainlesssteel tubing. For separations in the evaluation of the detector in theoxidative mode, a 6' × 1/4' foot glass column containing 3% OV-1 and 3%OV-210 on 80/100 mesh Gas Chrom Q was operated at 215° centigrade with anitrogen carrier gas flow rate of 40-50 cc/min (for helium a flow rateof 50 cc/min was utilized), with an inlet temperature of 230°centigrade. The conductivity solvent was 95-100% ethyl alcohol. Solventflow rate through the detector was 0.41 cc/min. For separations in theevaluation of the detector in the reductive mode, a similar glass columnon 80/100 mesh acid washed Chromosorb W was utilized with a furnacetemperature of 820° centigrade.

Detector response to chlorinated hydrocarbon pesticides in the reductivemode for 1 ng (FIG. 10A), 0.1 ng (FIG. 10B), and 0.05 ng (FIG. 10C) oflindane, heptachlor, aldrin, heptachlor epoxide, and dieldrin, in orderof elution, with a detector sensitivity of 0.2 μmho/mv. Detectorresponse for the same pesticides in the oxidative mode is shown for 1 ngwith detector sensitivity of 0.4 μmho/mv (FIG. 11A) and 0.1 ng withdetector sensitivity of 0.2 μmho/mv (FIG. 11B).

As can be seen from these illustrations, the detector of this inventionexhibits high sensitivity and stability, the detector being much moresensitive than heretofore known detectors such as, for example, theCoulson electrolytic conductivity detector. Selectivity (relative tohydrocarbon) is also extremely high. Detector response (peak height)versus grams of heptachlor is shown in FIG. 12.

A comparison of microelectrolytic conductivity and flame photometricresponses to sulfur containing compounds is shown in FIG. 13. The orderof elution is diazinon, malathion, and parathion with FIG. 13A showingthe electrolytic conductivity detector and FIG. 13B showing the flamephotometric detector. The electrolytic conductivity detector of thisinvention gives approximately 50% full scale deflection at 0.5% noisefor 5 ng of diazinon, malathion, and parathion. In contrast, the flamephotometric detector of the prior art gives only about 2% to 3%deflection at twice the noise level for the same quantity of compound.The electrolytic conductivity detector of this invention has highsensitivity to sulfur compounds and has wide linear dynamic range (theflame photometric detector's response is exponential with concentration)making it an attractive device for the analysis of sulfur containingpesticides and air pollutants.

Detector response for the preferred embodiment shown in FIGS. 3 and 5has been found to be at least as good as that shown for the detector inFIG. 8 as set forth hereinabove, and in many instances better. Thegraphs of FIG. 14 illustrate performance of the detector utilizing thepreferred embodiment of the separator-conductivity cell shown in FIGS. 3and 5. Detector response to chlorinated hydrocarbon pesticides in thereductive mode is shown, for illustrative purposes in FIG. 14. A Tracor550 as chromotograph was used, as were coiled glass columns with thesame packing as described hereinabove in conjunction with the detectorsystem producing the response indicated by the graphs as shown in FIGS.10-13. The column temperature was 185° centigrade and helium carrier gaswas used at a flow rate of 30 ml/mi. The furnace was operated at 850°centigrade with ˜/cc/min H₂ reaction gas. The quartz tube utilized was 3mm O.D.× 1 mm I.D. times 100 mm long, and solvent flow was 0.15 m1/minETOH with a sensitivity of 0.2 μmho/mv. Detector response is shown tochlorinated hydrocarbon pesticides in the reductive mode for 0.02 ng(FIG. 14A), 0.05 ng (FIG. 14B), 0.1 ng (FIG. 14C), and 0.2 ng (FIG. 14D)of lindane, heptachlor, aldrin, heptachlor epoxide, and dieldrin, inorder of elution.

From the foregoing, it can be seen that the electrolytic conductivitydetector of this invention provides an improved detector having aseparator and conductivity cell. The gas-liquid separator-conductivitycell is felt to operate on a different principle than known priordetectors in that the geometry and principle of operation as utilized inthe detector of this invention allows the dimensions to be easilyaltered as desired. The ability of the detector of this invention toutilize small quantities of solvent is advantageous because thesensitivity of detecting devices such as conductivity cell is inverselyproportional to the quantity of solvent utilized. This is shown to be afurther advantage of this invention since utilized quantities of solventmay be as low as 0.15 ml per minute while prior art devices requiredutilization of a minimum of 3 to 5 ml of water per minute, which canresult in a 20 to 30 fold increase in sensitivity of the electrolyticconductivity detector of this invention.

Thus, the electrolytic conductivity detector of this invention giveshigh performance, is easy to use, and is of small size and enables easymounting. In addition, since the detector has high sensitivity, it ismore useful than known devices of this type. Since the detector also hashigh selectivity and wide linear dynamic range, the detector is moreuseful in many instances than is the electron capture detector. Finally,the detector requires little maintenance and can be used trouble-freefor long periods of time.

The gas-liquid separator-conductivity cell makes the detector capable ofhigh performance and small size. The concentric tube separator does notrequire a minimum solvent flow rate for operation, and since the primaryforce that drives the solvent through the conductivity cell is thedownward force of the moving solvent, solvent flow rate through the cellapproaches zero as the total solvent flow rate approaches zero. Thus,the cell is always filled with solvent which prevents bubbles beinglodged between the closely spaced electrodes, which is advantageoussince the solvent often tends to channel around a bubble rather thandisplacing it.

The separator-conductivity cell functions efficiently and delivers asmooth solvent flow through the cell with solvent flow rates from 0.1 to1.0 cc/min and gas flow rates from 5 to 500 cc/min or more.

What is claimed is:
 1. An electolytic conductivity detector for gaschromatography, said detector comprising:compound supply means forproviding as an output therefrom compounds to be tested in the form ofeluant gases; forming means for receiving said eluant gases from saidcompound supply means and forming therefrom conductivity supportinginorganic gaseous molecules; solvent supply means for supplying anaqueous or organic solvent; contactor means for mixing substantiallyimmediately upon contact gaseous molecules received from said formingmeans with said solvent from said solvent supply means to form a mixturethereof; separator means for receiving said mixture from said contactormeans and substantially immediately separating said mixture into liquidand gas phases; and measuring means for receiving said liquid phase fromsaid separator means and measuring the conductivity of said liquidphase.
 2. The electrolytic conductivity detector of claim 1 wherein saiddetector is of small size with said contactor means, said separatormeans, and said measuring means being assembled as a single unit.
 3. Theelectrolytic conductivity detector claim 1 wherein said forming means isa furnace having an input receiving said eluant gases from said compoundsupply means for formation of compounds therefrom having small moleculesthat will support electrolytic conductivity, and wherein said detectorincludes reaction gas supply means also connected with said furnaceinput.
 4. The electrolytic conductivity detector system of claim 1wherein said measuring means includes a conductivity meter connectedwith said measuring means.
 5. The electrolytic conductivity detector ofclaim 4 wherein said measuring means also includes a recorder connectedwith said conductivity meter.
 6. The electrolytic conductivity detectorof claim 1 wherein said system also includes a solvent circulatingsystem for receiving liquid from said separating and measuring means andsupplying solvent to said mixing means.
 7. The electrolytic conductivitydetector of claim 6 wherein said solvent circulating system includes asolvent reservoir and a pump for withdrawing solvent from said reservoirand for controlling solvent delivery to said mixing means.
 8. Andelectrolytic conductivity detector for gas chromatography, said detectorcomprising:means for forming conductivity supporting molecules of acompound to be tested; means for mixing molecules received from saidforming means with a solvent to form a mixture; means for separatingsaid mixtured into liquid and gas phases, said separating meansincluding a reservoir for receiving said liquid phase; a conductivitycell; means for conducting said liquid phase from the reservoir of saidseparating means through said conductivity cell; and means for measuringthe conductivity of said liquid withdrawm from the reservoir of saidseparating means and passing through said conductivity cell.
 9. Theelectrolytic conductivity detector of claim 8 wherein said separatingmeans and said conductivity cell are mounted in contiguous side by sidepositions, and wherein said system includes a rugged housing forprotecting said separating means and conductivity cell.
 10. Theelectrolytic conductivity detector of claim 9 wherein said housing iscylindrical and of a size no greater than about one inch in diameter andtwo inches in length.
 11. An electrolytic detector for gaschromatography, said detector comprising:a furnace for formingconductivity supporting gaseous molecules of a compound to be tested; asolvent supply means supplying an aqueous or organic solvent; agas-liquid contactor means for receiving said molecules from saidfurnace and solvent from said solvent supply means and substantiallyimmediately mixing the same to form a mixture thereof; a gas-liquidseparator and conductivity measuring cell for receiving said mixturefrom said contactor means and substantially immediately separating thesame into liquid and gas phases and measuring the conductivity of saidliquid phase, said separator and measuring cell including a reservoirfor receiving said liquid phase to measured; and means for indicatingthe conductivity of liquid phase while in said separator andconductivity cell as sensed at said conductivity measuring cell.